Modeling a hydroelectric turbine: exporting the Heliciel turbine to Mecaflux Pro3D

The flow of a hydroelectric installation depends on the pitch of the turbine blades and on its rotation speed. This tool exports your turbine as a Mecaflux Pro3D singular element: a head loss whose coefficient varies with rpm and pitch. Inserted into a gravity network modeled with Pro3D, this element simulates the flow through the turbine and shows the flow rate resulting from the pitch and speed settings.

• Steps:

1. What the exported element contains
2. The operating range swept
3. Step 1: compute the head loss coefficients
4. Step 2: the B-spline surface and the .elsin export
5. Variant: exporting a stator or a pump
6. In Mecaflux Pro3D

1: What the exported element contains

For each tested operating point, Heliciel computes the turbine off-design and reads its head loss coefficient: the ratio between the upstream-downstream pressure difference created by the runner and the upstream dynamic pressure. This is the quantity Mecaflux Pro3D expects from a singular element. The exported element carries this coefficient as a function of two variables, rotation_rpm and calage_deg (pitch), with their bounds, and the turbine inlet diameter (the runner diameter).

The menu entry, under File

2: The operating range swept

On opening, the window restores the project design point and proposes a reference name built from the turbine: number of blades, tip and root radii, rpm and nominal flow (Turbine_B4_R1000mm_r600mm_53rpm_43200m3h for instance). The swept range is centered on the operating point:

• 5 rotation speeds, spread on both sides of the nominal rpm in steps of one fifth of that rpm (i.e. from 0.6 to 1.4 times the nominal rpm);
• 5 pitch settings, from −20° to +20° around the nominal tip pitch, in 10° steps.

That is 25 operating points. The bounds are displayed in the window (min and max rpm, min and max pitch, nominal flow in m³/h) before starting the calculation.

The operating range, before calculation

3: Step 1: compute the head loss coefficients

The button Calculate coefficients of head losses from the use range chains the 25 calculations: for each rpm, Heliciel updates the off-design performance, then varies the pitch through the pitch variator of the 3D view and reads the coefficient at each step. Progress is displayed (test n/25, current rpm and pitch) and the coefficient list fills up as it goes. The computing time is that of 25 off-design calculations.

The coefficients read, rpm by rpm

4: Step 2: the B-spline surface and the .elsin export

The 25 coefficients are interpolated by a B-spline surface as a function of rpm and pitch: this is what Pro3D will query between the computed points. The See B_spline surface coefficient button displays it for checking. The Export to mecaflux Pro3D format .Elsin button asks for the element name and saves it in the Pro3D library: Documents Mecaflux Pro3D\bibliotheque\singuliers\turbines. If that folder does not exist on the computer, the file is written to the desktop and a message says so, for manual insertion.

The B-spline surface of the coefficient

5: Variant: exporting a stator or a pump

The same menu offers Export Stator (propeller 0.01 Rpm) to Mecaflux Pro3D and Export pump/Fan to Mecaflux Pro3D, for ducted propulsion propeller projects. A stator is a propeller that does not rotate: the rpm is set to 0.01 to simulate zero rotation, and the swept range reduces to 7 pitch settings, from −30° to +30° in 10° steps. This is how a fixed-vane distributor or a straightening grid is exported to a Pro3D network.

6: In Mecaflux Pro3D

The .elsin element appears in the Pro3D singular element library, turbines category. Inserted into a gravity network between the upstream reservoir and the downstream basin, it receives the flow the network imposes and opposes the runner head loss at its rotation_rpm and calage_deg variables. Varying these two variables means reading the installation flow for each turbine setting.

To size the complete structure around the runner — spiral casing, distributor, draft tube, piezometric line — see Hydro Turbine design; for the design of the runner itself, the hydraulic turbine pages and the micro Kaplan turbine tutorial.